1. Field of the Invention
The present invention relates to a chain transmission assembly suited to suppressing the occurrence of noise and making an assembly light in weight.
2. Description of Background Art
The following is a description of the meshing of sprocket teeth and rollers of a roller chain for a chain transmission assembly where a roller chain is wrapped around a sprocket. FIG. 8(a) to FIG. 8(c) are explanatory views showing the operation in the state where a related sprocket and roller chain mesh.
In FIG. 8(a), a sprocket 100, with a center of rotation 101 of the sprocket 100, includes teeth 102 . . . (where . . . shows a plurality of items, with the same being the case hereafter) of the sprocket 100, teeth bottoms 103 . . . of the of the sprocket 100, roll chain link plates 104 shown by an imaginary line (only one shown), roller chain rollers 105 and 106, and centers of rotation 107 and 108 of the rollers 105 and 106. In FIG. 8(a), the teeth bottoms 103 of the sprockets 100 are positioned just above the centers of rotation 101 and the rollers 105 mesh with the teeth bottoms 103.
In FIG. 8(b), when the sprockets 100 rotate by an angle of xcex81 in an counterclockwise direction from the state in FIG. 8(a), the rollers 105 move while remaining meshed with the teeth bottoms 103 of the sprocket 100 and the centers of rotation 107 of the rollers 105 fall by just a distance xe2x88x9d1 from the position of FIG. 8(a).
At this time, the rollers 105 and 106 move in an integral manner so that the roller chain goes from being loose to being tense, and the center of rotation of the roller 106 falls just by a distance xe2x88x9d1 together with the dropping of the roller 105.
In FIG. 8(c), the sprocket 100 rotates further in the counter-clockwise direction so that when the sprocket 100 rotates by an angle xcex82 from the state shown in FIG. 8(a), in addition to the rollers 105 and the teeth bottoms 103 of the sprocket 100 meshing, the rollers 106 meshes with the teeth bottoms 103.
The teeth bottoms 103 collide with the rollers 106 at this time so that a noise therefore occurs due to these collisions.
In this case, the centers of rotation 107 and 108 of the rollers 105 and 106 fall just by xe2x88x9d2 from the position of FIG. 8(a), and the distance between the center of rotation 101 of the sprocket 100 and the centers of rotation 107 and 108 of the rollers 105 and 106 becomes R cos xcex82. The wrapping radius of the roller chain in this case is R cos xcex82, and an amount of vibration xe2x88x9d2 of the roller chain in a vertical direction xe2x88x9d2 is 2=R-R cos xcex82.
In the above, when a roller chain meshes with the sprocket 100, noise is generated by the teeth bottoms 103 of the sprocket 100 and by the rollers 106 and the wrapping radius of the roller chain changes from R cos xcex82 to R. The vibration of the roller chain is therefore substantial, and noise is therefore generated from the roller chain itself.
A chain transmission assembly combining a sprocket having a resilient member and a roller chain as shown in the following is well-known for reducing this kind of noise.
FIGS. 9(a)-9(b) are an operational view illustrating the state of meshing of a related sprocket having a resilient member and a roller chain. This configuration is substantially the same as the configuration shown in FIGS. 8(a)-8(c) and, the same numerals are applied therein after. A detailed description of the common elements is omitted.
In FIG. 9(a), are annular resilient members 110 are fitted to a side of the sprocket 100, rollers 111 are fitted in a freely rotatable manner to further link plates (not shown) for supporting the rollers 105 in a freely rotatable manner, and the rollers 111 are provided with centers of rotation 112.
In FIGS. 9(a)-9(c), the teeth bottoms 103 of the sprocket 100 are positioned just above the centers of rotation 101.
The position of the rollers 105 is decided by the rollers 111 meshing with the resilient members 110 and the teeth bottoms 103 so that edges of the link plates 104 collide with the resilient members 110 and the rollers 105 therefore float from the teeth bottoms 103 of the sprockets 100.
The wrapping radius of the roller chain in this case is taken to be (R+d1). The portions where the link plates 104 and the resilient members 110 overlap, i.e. the portions where the resilient members 110 are pushed so as to be compressed by the edge of the link plate 104, are subjected to hatching.
In FIG. 9(b), when the sprocket 100 rotates by an angle of xcex81 in an counter-clockwise direction from the state in FIG. 9(a), the rollers 105 and 106 move in an integral manner, the link plates 104 press and compress the resilient members 110, and the centers of rotation 107 of the rollers 105 and the centers of rotation 108 of the rollers 106 fall by just a distance xcex21 from the position of FIG. 9(a).
In FIG. 9(c), when the sprocket 100 rotates in an counter-clockwise direction so as to give rotation through an angle xcex82 from the state in FIG. 9(a), the teeth 102 become positioned just above the centers of rotation 101 and, the resilient bodies 110 are further compressed by a coercive force of the link plates 104 occurring due to the tension of the roller chain. The rollers 105 then mesh with the teeth bottoms 103 and the rollers 106 also mesh with the teeth bottoms 103 due to the compression of the resilient body 110.
The wrapping radius of the roller chain in this case is R cos xcex82, and an amount of vibration of the roller chain in a vertical direction xcex22 is xcex22=R+d1-R cos xcex82.
At this time, the link plates 104 collide with the resilient members 110 before the rollers 105 and 106 collide with the teeth bottoms 103 and the noise occurring when the rollers 105 and 106 collide with the teeth bottoms 103 is therefore absorbed.
FIG. 10 is a graph illustrating changes in wrapping radius of a related sprocket and also shows changes in the wrapping radius of the roller chain for the sprocket with no resilient body described in FIGS. 8(a)-(c) and the sprocket with a resilient body described in FIGS. 9(a)-(c), with the vertical axis showing a wrapping radius and the horizontal axis showing time.
The wrapping radius changes from R cos xcex82 to R for the sprocket with no resilient body shown by the broken lines.
The wrapping radius changes from R cos xcex82 to R(d+1) for the sprocket with a resilient body shown by the dashed lines.
From the above, with the sprocket 100 with the resilient body, an amount of vertical vibration d1 of the roller chain becomes larger to the extent of d1=xcex22xe2x88x92xcex12 compared to the sprocket 100 with the resilient body due to the resilient body 110. This means that there is little reduction in noise due to the collisions of the teeth bottoms 103 and the rollers 106 or in noise due to vibration of the roller chain itself.
A chain transmission apparatus for reducing noise and improving quality based on a chain transmission assembly that combines a sprocket having a resilient member 110 and a roller chain as described in FIGS. 9(a)-9(c) is disclosed in, for example, Japanese Laid-open Patent Publication No. Sho. 61-82164 entitled xe2x80x9cQuiet Chain Approximation,xe2x80x9d Japanese Patent Laid-open Publication No. Hei. 63-214566 entitled xe2x80x9csprocket,xe2x80x9d and Japanese Patent Laid-open Publication No. Sho. 63-251654 entitled xe2x80x9cChain-Type Transmission Assembly.xe2x80x9d
In FIG. 1 of aforementioned publication No. Sho. 61-82164, a shock-absorbing ring 15 composed of a resilient body is fitted to a boss 14 of a sprocket b, link plates 11 of a roller chain a and formed in a substantially oval shape. A roller chain a meshes with a sprocket b to provide a quiet chain mechanism.
Further, in FIG. 3 of aforementioned publication No. Hei 63-214566, a chain 6 with link plates 6a are formed in an hourglass-shape. A sprocket 3, is provided wherein a side includes a resilient body 13 so that the chain 6 with an outer periphery of a wave shape makes contact in a uniform manner. In FIG. 5 of this publication, a chain formed by the hourglass-shaped link plates 106a and a sprocket, are provided wherein a side of the sprocket is fitted with an annular resilient body 113.
In FIG. 3 of aforementioned publication No. Sho. 63-251654, a chain type transmission assembly is disclosed wherein rolling plates 19 of a roller chain 13 are flat and oval in shape, pin link plates 21 are shaped like an hourglass, and a drive sprocket 11 is provided with an annular resilient body 17, and end surfaces 19a of the roller link plates 19 collide with the annular resilient body 17.
With the technology in aforementioned publication No. Sho. 62-82164, the cross-sectional area of a central part is larger than other portions at a central part in a direction orthogonal to a longitudinal direction of the link plates 11 because the link plates 11 are substantially orthogonal. The tensile strength in the case where tensile force acts via two pins 12 at the link plates 11 is therefore at a maximum at a central section, this central section therefore has to be stronger than necessary, and the weight of the assembly therefore increases.
With the technology of aforementioned publication No. Hei. 63-214566, with the combination of the resilient body 13 and the link plate 6a, an outer peripheral section at the pins at two locations of the link plate 6a collide with the resilient member 13 in a substantially uniform manner. The original tension of the chain 6 is therefore substantial in order to take into consideration the generation of noise due to the vibration of the chain itself as set forth in the combination of the annular resilient body 113 and the link plate 106a shown in FIG. 5 of this publication.
With the technology in publication No. Sho. 63-251654, when roller link plates 19 of the roller chain 13 collide with the annular resilient body 17 of the drive sprocket 11, striking of the drive sprocket 11 and the roller chain 13 is suppressed the structure is such that pin link plates 21 of the roller chain 13 do not strike the annular resilient body 17. Consideration therefore has to be given to the occurrence of noise due to the colliding of the drive sprocket 11 and the roller chain 13 at portions of the pin link plates 21.
Further, because the roller link plates 19 are flat and oval in shape, the weight of the roller chain 13 also increases.
It is therefore an object of the present invention to provide a chain transmission assembly capable of effectively suppressing the occurrence of noise at the time of meshing of a sprocket and a roller chain, while making a roller chain light in weight.
In order to achieve this object, a chain transmission assembly is provided, that is fitted with an annular resilient member at a side of a sprocket, with edges of hourglass-shaped link plates of a roller chain wrapped around the sprocket being received by the resilient body, and with the resilient body absorbing noise occurring when the roller chain meshes with the sprocket, wherein projections colliding with constricted portions at the centers of the hourglass-shaped link plates are provided at the resilient body.
By having projections collide with constricted portions at the centers of hourglass-shaped link plates, when the roller chain starts to mesh with the sprocket, the edges of a hourglass-shaped link plates of the roller chain are pushed radially outwardly by the projections of the resilient member.
As a result, the amplitude of vibrations occurring as a result of the roller chain meshing with a sprocket can be made small, vibrations of each part of the roller chain can be made small, and noise emanating from the chain itself can be suppressed.
Further, the collision speed at the time when rollers of the roller chain collide with the teeth bottoms of the sprocket can be reduced and the occurrence of noise due to these collisions can be suppressed.
Moreover, because an hourglass-shaped link plate is used, the link plate can be made lighter than when using a flat and oval shaped or oval shaped link plate and the roller chain can therefore also be made lightweight.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.